The invention herein described was made in the course of or under a contract or sub-contract thereunder with the Department of the Army.
1. Field of the Invention
The present invention relates generally to the field of non-aqueous electrochemical cells and, more particularly, to electrolyte additives which improve stability and inhibit anode passivation and corrosion in such cells.
2. Description of the Prior Art
Much work has been done in the field of high energy battery systems utilizing highly reactive anode materials such as alkali or alkaline earth metals in combination with non-aqueous electrolytes. The electrolyte is normally composed of a solute which is commonly a metal salt or a complexmetal salt of the anode material dissolved in a compatible non-aqueous solvent depolarizer such as SOCl.sub.2. An inert/cathode, usually of carbon black, is also used in such cells. In order to increase the rate capability of such cells, cathode dopants or catalyists such as transition metal macrocyclic complexes have been utilized and conjunction with the cathodes. These include, for example, transition metal macrocyclic complexes of phthalocyanines, Schiff's base and certain porphyrins.
The cells are of two basic types, namely, active and reserve. Active cells are those in which the electrochemical couple of the cell is always in an operative state after assembly of the cell, i.e., both electrodes are in contact with the electrolyte at all times. Reserve cells, on the other hand, are cells in which at least one component of the cell necessary to produce current between the electrodes, normally the electrolyte, is separately contained or isolated from the others, as by storing the electrolyte in a glass ampule, thereby rendering the cell inoperative. The cell is stored in the inoperative state and is activated at the desired time by an external event such as a sudden impact which ruptures the ampule. This allows the electrolyte to flow throughout the cell to complete the internal circuit.
The potential uses of electrochemical couples such as those mentioned above in high rate, high power batteries have not been fully realized, however, partially because of the very limited life of active cells. In the case of lithium/thionyl chloride systems, reactions between the lithium anode and the electrolyte medium or species in the electrolyte medium result in passivation of the anode and even corrosion or destruction of the anode after a relatively short period of time. This is especially true if metal organic complexes or dopants are utilized with respect to the cathode which have some soluability in the electrolyte medium.
In the prior art, sulfur dioxide and lithium oxide have been utilized in the electrolyte to assist in controlling passivating film growth on the anode which occurs upon exposure to the electrolyte medium when such cells are activated. Another technique utilizes precoating of the anode with polymers such as vinyl chloride, acrylcyanonitriles or the like. This however prevents anode passivation only during the initial active stand of the cells. Once these cells are subjected to load, the coating film will disintegrate and leave the anode unprotected from further passivation and corrosion.